1. Technical Field
The present invention generally relates to an image forming device, such as a copier or a printer or the like, which uses an electrophotographic method. More particularly, the present invention relates to an image forming device having a contact-charging type charging roller which, while rotating in contact with an image carrier which is driven to rotate, charges the surface of the image carrier, and a cleaning member for the charging roller.
2. Related Art
Conventionally, devices utilizing corona discharge development, such as scorotron chargers, have been used as charging devices of image forming devices such as copiers or printers or the like which adopt an electrophotographic method. However, in the case of a charging device which uses corona discharge development, the generating of ozone and nitrogen oxides, which adversely affect human bodies and the global environment, is problematic. In contrast, with a contact-charging method which carries out charging of an image carrier by causing an electrically-conductive charging roller to directly contact an image carrier, the generating of ozone and nitrogen oxides is greatly decreased, and the power efficiency thereof is also good. Therefore, the contact-charging type method has become the mainstream method recently.
In such a contact-charging method charging device, because the charging roller is always contacting the image carrier, there is the problem that it is easy for contamination due to foreign matter adhering to the surface of the charging roller to arise. At the downstream side of the transfer process, the surface of the image carrier, at which the image forming operation is repeatedly carried out, goes through a cleaning process which removes foreign matter such as residual toner and the like after the transfer. Thereafter, the surface of the image carrier enters into the area of the charging process. However, even after going through the cleaning process, minute particles which are smaller than the toner, such as portions of the toner or external additives of the toner or the like, remain on the image carrier without being cleaned, and adhere to the surface of the charging roller. The foreign matter adhering to the surface of the charging roller causes non-uniformity in the surface resistance value of the charging roller, and abnormal discharging or unstable discharging occurs, and the uniformity of charging deteriorates.
In order to overcome this problem, there has been proposed a technique in which a cleaning member, which is formed from a plate-shaped sponge or a brush or the like, is made to press-contact (slidingly-contact) the surface of a charging roller which rotates, so as to clean the contamination on the surface of the charging roller. In this technique, the charging roller is rotatably supported at a housing (case), is urged by an urging member (spring) to press-contact a photosensitive body, and is thereby rotated by the photosensitive body. The cleaning member as well is urged by a separate urging member to press-contact the charging roller.
However, in the structure of the above-described technique, if errors in the precision of the alignment or changes over time arise between the charging roller and the cleaning member, or if flexure arises due to the press-contact force applied to each member, galling arises between the shaft-receiving portions and the end portions (supporting portions) of the rotating shaft of the charging roller, and the end portions locally contact the shaft-receiving portions strongly. Therefore, the rotation resistance increases, the ability of the charging roller to move following the photosensitive body deteriorates, and it is easy for defects in charging to arise. Further, in a structure in which the cleaning member is not a fixed-contact-type as in this technique, and rather is, for example, a rotating-contact-type which is rotated by the charging roller, due to the aforementioned poor alignment between the members or flexure caused by the application of press-contact force, the end portions (supporting portions) of the rotating shaft of the cleaning member locally contact the shaft-receiving portions strongly in the same way as at the charging roller. Therefore, the problem arises that the ability of the cleaning member to move following the charging roller deteriorates, leading to a deterioration in the cleaning ability.